This invention relates to a method for identifying isotopes in gas to be measured(hereinafter, referred to as xe2x80x9csample gasxe2x80x9d) or for analysing abundance ratio and concentration thereof with high accuracy and sensitivity from absorption spectra of sample gas on which the spectra are measured by using a semiconductor laser beam.
In a medical field, diagnosing and grasping conditions of sorts of organs of the body is carried out by giving stable isotopes to the body and analysing isotopes contained in exhausted expiration. For example, a method for examining 13C-urea expiration has been recently used to diagnose whether the body is infected with Helicobacter pylori bacteria or not with relation between gastritis or gastric ulcer and gastric infection with Helicobacter pylori bacteria. This is a method for analysing conditions of patient""s organs by measuring amount of 13CO2 gas contained in patient""s expiration after giving a 13CO-marked compound to the patient who suffers gastritis or gastric ulcer.
For this, the method for examining 13C-urea expiration requires means for analysing stable isotopes appropriately. A mass spectroscopy and a method for an infrared spectroscopic analysis using an infrared lamp or the like are known as methods for analysing the isotopes.
However, the mass spectroscopy has problems of complexity in operating the apparatus and high cost of the apparatus, while analysing isotopes with high accuracy. Thus, the method for an infrared spectroscopic analysis has been generally adopted which uses a small difference between absorption wavelengths in relation with infrared rays of 13C/12C, caused by the difference between mass of isotopes 13C/12C. A spectroscopic analyser using an infrared lamp used in a method for an infrared spectroscopic analysis has many uses because of its convenience and low cost but has low accuracy so that a spectroscopic method for analysing isotopes by using a semiconductor laser which oscillates a beam having a 1570 nm(10xe2x88x929 m)-band wavelength has been recently suggested.
But, this wavelength of 1570 nm(10xe2x88x929 m)-band zone has a small absorption coefficient of carbon dioxide gas(CO2) so that a high sensitive analysis is hardly achieved. Thus, a preparatory process such as a concentrating process using an absorbent absorbing CO2 gas contained in expiration at a lower temperature has been performed in order to increase sensitivity. Moreover, the wavelength band is the zone in which various kinds of molecules are absorbed and in which there exist a plurality of adjacent absorption line peaks of isotopes so that it is difficult to specify absorption lines of isotopes 13C/12C to be measured. Because of that, the isotopes 13C/12C are identified through measuring by using various kinds of gases that the respective concentrations of the isotopes 13C/12C are varied.
A spectroscopic method for analysing isotopes by using a semiconductor laser having a wavelength zone of 2000 nm(1990xcx9c2060 nm) band has been recently under development. In this wavelength zone, an absorption intensities of isotopes 13C/12C are greater than those of 1570 nm-band zone by two digits and sensitivities thereof are accordingly greater by about two digits. And it is appreciated that the new method has an advantage that a preparatory process concentrating isotopes which is required in the spectroscopic analysis of 1570 nm-band zone in order to increase a sensitivity is not required. Therefore, in a spectroscopic method for analysing isotopes, the inventors of the present invention aimed at using a semiconductor laser beam having a 2000 nm-band zone based on the aforementioned advantage and it is an object of the present invention to provide a spectroscopic method for analysing isotopes in order to identify isotopes and carry out quantitative analysis with high accuracy and sensitivity with a simple system accurately distributing the semiconductor laser beam having 2000 nm-band zone.
In order to achieve the above mentioned object, the first aspect according to the present invention provides a spectroscopic method for analysing isotopes contained in gas to be measured by identifying and quantitatively measuring isotopes by using wavelengths of absorption spectra absorbed in existence of said isotopes, the improvement is characterized in that the method comprises the steps of using a semiconductor laser beam as a beam source for said wavelengths of said absorption spectra; and using a reference gas for identification of said isotopes, wherein said reference gas contains collating components having two wavelengths of well-known absorption spectra in wavelength band close to said wavelengths of absorption spectra of said isotopes.
Furthermore, the second aspect according to the present invention provides the spectroscopic method for analysing isotopes according to the first aspect, wherein said collating components contained in said reference gas is hydrogen bromide; and said collating components of said two wavelengths of said well-known reference absorption spectra are H79Br and H81Br.
Furthermore, the third aspect according to the present invention provides the spectroscopic method for analysing isotopes according to the first or the second aspect, wherein said isotopes to be measured are isotopes of carbon dioxide gas.
Furthermore, the fourth aspect according to the present invention provides the spectroscopic method for analysing isotopes as in any of the preceeding aspects, wherein said semiconductor laser beam source emits spectra having wavelength zone of 2000 nm band.
Furthermore, the fifth aspect according to the present invention provides the spectroscopic method for analyzing isotopes according to the third or the fourth aspect, wherein said said isotopes of carbon dioxide gas as sample gas are 12CO2 and 13CO2 and said 12CO2 and 13CO2have pairs of the following wavelengths
(a wavelength of isotope 12C2(nm)):(a wavelength of isotope 13CO2(nm))
2054.37:2053.96
2044:2044.49
2035.34:2035.63
2010.18:2010.29
2002.51:2002.54
1995.99:1996.10
and a abundance ratio is measured by an absorbance in accordance with said a respective pair of wavelengths.
Furthermore, the sixth aspect according to the present invention provides the spectroscopic method for analysing isotopes by using a semiconductor, is which comprises the steps of identifying said isotopes by using absorption spectra of hydrogen bromide as reference gas having well-known collating components, said absorption spectra having wavelength band according to the fourth aspect; and identifying existence of impurities generating absorption spectra at said wavelength band.